Ensure that the ApiErrorCode type is exported

src/index.ts

@@ -1,5 +1,5 @@
 export { OwlBoardClient } from './lib/client.js';
-export { ValidationError, ApiError } from './lib/errors.js';
+export { ValidationError, ApiError, type ApiErrorCode } from './lib/errors.js';
 
 // Re-export API Schema types
 export type * from '@owlboard/api-schema-types'